Luminescent ammunition marking with the Eu(btfa)3bipy complex: gunshot residue detection and prospects for time-since-discharge estimation

Abstract

The detection of gunshot residues (GSR) from non-toxic ammunition represents a significant challenge in forensic science due to the absence of metallic elements traditionally used as markers. In this context, the incorporation of luminescent markers into ammunition has emerged as a promising alternative. In this work, the β-diketonate complex Eu(btfa)₃bipy was synthesized via a scalable reflux method, characterized, and evaluated as GSR marker. The coordination of the Eu³⁺ ion to the ligands was confirmed by FTIR, and SEM analysis revealed crystallization into irregular three-dimensional blocks. Under UV radiation, the complex exhibited intense red emission, with the ⁵D₀→⁷F₂ transition being the most prominent. It also showed high quantum efficiency (74 %). After discharge of ammunition containing the complex, luminescent gunshot residues (LGSR) were clearly visible on the shooter's hand, firearm, and target, using only a low-power portable UV lamp. SEM/EDS analysis confirmed the presence of both conventional GSR and Eu(btfa)₃bipy complex, which maintained its original morphology after firing. Additionally, LGSR retained the characteristic ⁵D₀→⁷F_J transition of Eu³⁺ ion even after discharge. Finally, the photostability of the complex under prolonged irradiation was assessed using two distinct light sources. The excitation spectra and asymmetry ratio (R) were found to be dependent on irradiation time. Although further studies are needed, the observed spectral changes may support estimation of the time since discharge. These findings highlight a new forensic application for the Eu³⁺ complex, combining visual detection, chemical identification, and time-since-discharge estimation in a single system.